1. Field of Invention
The present invention relates to equipment utilized during measurement while drilling (MWD) data retrieval in subterranean wells. In particular, the invention relates to filtering apparatus and related methods for preventing debris from entering sensitive areas in a drilling system such as a turbine power source used to operate directional sensors, while maintaining desired flow rates for optimal drilling.
2. Description of the Related Art
Horizontal (directional) drilling continues to prove to be an extremely efficient method for retrieving oil. Conventional vertical wells are limited by surface land formations limiting possible rig set up, and subterranean oil formations that are extremely difficult to extrapolate through conventional methods for maximum oil production. Horizontal drilling offers a solution to many complications currently faced through conventional vertical wells. Some of the most important pieces of equipment required in horizontal drilling are directional sensors located at the distal end of a drill string that transmit vital survey, formation, and performance data to the surface without requiring costly down time. The directional sensors require local power which is commonly provided by turbine alternators which are located near the directional sensors in the drill string. The turbine alternators are operated by circulating drilling mud through the drill string and into a turbine causing the turbine to spin thereby generating electricity to power the directional sensors. Turbine alternators are preferred over alternative battery power sources because they generally offer a more effective power source with a longer operating life.
It is well known that the turbines within such alternators are highly sensitive. If a turbine is damaged, a power failure may occur resulting in loss of electricity to the directional sensors. This can bring horizontal drilling operations to a halt until the turbines are repaired or replaced, which can be a very expensive and time consuming process since it requires removal of the entire drill string from the well, repair/replacement of the turbine alternators, and reinsertion of the drill string into the well. It is therefore important to avoid such extended down time.
In order to protect the turbines and limit potential power failures to the directional sensors, a MWD drill pipe screen or mud screen is ordinarily placed at the top of the drill string to control debris from entering the drill string and finding its way to the vital turbine alternators. It is to be appreciated that when such a screen or filter becomes clogged, there is usually an associated spike in the pressure of the drilling mud used to operate the turbines. When such a spike is noticed, it is a signal to the drilling operators to change the screen, or risk damage to the drill string from buildup of excessive pressure. Replacing the drill pipe screen is a cumbersome process, requiring drilling operations to be shut down while the filter is removed, cleaned and/or replaced, but this preferable to a blowout from excessive pressure, or causing damage to the turbines at the other end of the drill string.
Existing drill pipe screens include spiral drill pipe screens, bar/rod drill pipe screens, slotted tube drill pipe screens, and perforated drill pipe screens. However, each of these types of drill pipe screen suffers from one or more disadvantages. For example and without limitation, existing drill pipe screens (particularly spiral and slotted tube screens) tend to clog readily, and may cause a spike in drilling mud pressure after a relatively short period of time (e.g., 2-3 runs). In addition, existing drill pipe screens may cause small pressure spikes even though the screen may not be completely clogged, forcing the drilling operators to stop operations to check the status of the screen only to find that it is not significantly clogged and operations could have continued. This results in unnecessary downtime to check and thereafter clean or replace a drill pipe screen that did not actually need to be serviced. Current screens also suffer extensive failures due to damage sustained to the base metal of the screen (particularly bar-rod and perforated screens) allowing debris to pass through the screen and reach the sensitive turbine, potentially causing serious damage and drilling down time, and loss of drilling mud circulation which affects all drilling processes.
The oil and gas industry continues to streamline drilling processes with a keen eye on safety and cost management. However, as vital as drill pipe screens are to horizontal drilling, screen designs have not changed in the industry for an extended length of time. As horizontal drilling proves to be an effective method of drilling, a need has arisen for improved MWD drill pipe screens and related methods that maximize necessary drilling mud circulation, that are strong and reliable in order to provide substantial debris filtration, and that perform for extended periods of time without removal, repair or replacement in order to maximize efficiency and reduce costs.